Adjustment feedback method for improving silicon wafer flatness stability

Abstract

This invention relates to an adjustment feedback method for improving the flatness stability of silicon wafers, belonging to the field of silicon wafer processing technology. The method includes the following steps: Step 1: Before polishing, the silicon wafers are measured using equipment to screen out those that do not meet requirements and sort them by thickness. Then, a double-sided polishing method is used. Step 2: During polishing, slight fluctuations in polishing slurry temperature, slurry pH, slurry flow rate, removal rate, and stationary cooling temperature need to be controlled. Step 3: Measurement feedback adjustment is performed to monitor and adjust the flatness level fluctuations and silicon wafer thickness morphology. Step 4: When the silicon wafer is processed and flatness is measured, the equipment is adjusted according to the set target value. Step 5: Through software analysis, the thickness morphology of the measured silicon wafers is monitored to ensure that the processed silicon wafers have consistent thickness morphology. This method features convenient operation and good operational stability, solving the problem of poor flatness fluctuation stability during processing.

Description

Technical Field

[0001] This invention relates to the field of silicon wafer processing technology, and more specifically to an adjustment feedback method for improving the flatness stability of silicon wafers. Background Technology

[0002] With the continuous development of information technology, chip integration is becoming increasingly sophisticated, placing ever more stringent demands on manufacturing processes. Chip manufacturing processes can only evolve towards narrower dimensions, integrating more devices while reducing power consumption. This places extremely stringent requirements on the flatness of the photolithography process; even the slightest fluctuation can cause defects during processing. Chemical mechanical polishing (CMP) utilizes a chemical solution containing extremely fine abrasive particles to react with the surface being processed, altering the surface's chemical bonds to generate products that are easily removed mechanically. These chemical reactants are then removed through mechanical friction to achieve an ultra-smooth, damage-free, flattened surface. However, because this process utilizes a combination of chemical and mechanical actions for polishing, it suffers from drawbacks such as numerous process parameters and process instability.

[0003] It is difficult to guarantee complete uniformity of silicon wafers during polishing, and they will fluctuate within a certain range. Addressing these fluctuations and improving wafer flatness consistency is crucial for enhancing device quality. Current flatness improvement methods primarily involve modifications to the polishing equipment itself, such as precise control systems, electrical controls, and temperature controls; the selection and application of slurry; and optimization of the trimming process. However, these methods are costly, complex to control, and result in significant fluctuations in flatness levels. Therefore, it is essential to find methods to improve the stability of wafer polishing flatness to address these technical problems in existing technologies. Summary of the Invention

[0004] This invention primarily addresses the shortcomings of existing technologies by providing an adjustment feedback method for improving the flatness stability of silicon wafers. This method is characterized by its ease of operation and high stability. It solves the problem of poor flatness fluctuation stability during processing. By checking silicon wafer warpage and thickness before polishing, monitoring key processing parameters, and real-time monitoring of flatness levels after polishing, the stability of the silicon wafer flatness process is ensured.

[0005] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0006] An adjustment feedback method for improving the flatness stability of silicon wafers includes the following steps:

[0007] Step 1: Warp control and thickness control before polishing. Before polishing, the silicon wafers are measured by the equipment to screen out those that do not meet the requirements and sort them by thickness to avoid fluctuations in flatness after polishing. Then, double-sided polishing is used.

[0008] During polishing, a chemical solution containing extremely fine abrasive particles is used to react with the surface being processed, thereby changing the chemical bonds on the surface and generating products that are easily removed by mechanical means. The chemical reactants are then removed by mechanical friction to obtain an ultra-smooth, damage-free, flattened surface.

[0009] The second step: During the polishing process, it is necessary to control slight fluctuations in the polishing slurry temperature, polishing slurry pH, polishing slurry flow rate, removal rate, and plate cooling temperature.

[0010] Step 3: Perform measurement feedback adjustments to monitor and adjust the flatness level fluctuations and silicon wafer thickness morphology.

[0011] Step 4: When the silicon wafer is processed and its flatness is measured, the equipment is adjusted by setting the target value.

[0012] Step 5: Through software analysis, monitor the thickness and morphology of the measured silicon wafers to ensure that the processed silicon wafers have consistent thickness and morphology.

[0013] As a preferred option, silicon wafer warpage has a significant impact on flatness, especially the morphology after wire cutting; the average warpage deformation after wire cutting is required to be less than 8 μm.

[0014] As a preferred option, the requirements for the cutting edge are: V-shaped cutting edge with an included angle greater than 90°; L-shaped cutting edge with an included angle greater than 45°.

[0015] Preferably, 15 silicon wafers are processed simultaneously in each batch, and the amount of material removed is controlled by laser thickness measurement. If the thickness uniformity of the 15 silicon wafers is >0.8μm, there will be significant fluctuations in the flatness among the 15 silicon wafers.

[0016] Preferably, the FDC system monitors and alarms parameters such as polishing slurry temperature, polishing slurry pH, polishing slurry flow rate, removal rate, and stationary cooling temperature. Polishing slurry temperature fluctuations are limited to <0.5℃, pH <0.2, flow rate <0.4L / min, removal rate >0.5μm / min, and stationary cooling temperature <0.2℃. This ensures equipment operational stability during processing and guarantees stable silicon wafer flatness.

[0017] Preferably, when the TTV measurement changes by more than 40 nm compared to the previous batch, the machine should make appropriate corrections. If the change is +40 nm, the corresponding method is to decrease the target thickness by 0.1 μm, and vice versa.

[0018] As a preferred method, the silicon wafer is divided into different radial regions with R1=80, R2=100, and R3=140. Each region is divided into four quadrants, and the thickness of each quadrant is calculated separately; when there is a large deviation in the thickness morphology, the thickness value of the region will fluctuate.

[0019] As a preferred option, radial calculations must satisfy ATR1>ATR2>ATR3>0; ATR1 is AVTHKR1, the average thickness of the R1 circle; ATR2 is the average thickness within the R2-R1 pattern; and ATR3 is the average thickness within the R3-R2 pattern.

[0020] As a preferred method, regional calculations must meet the following requirements. X1 equals the average thickness in quadrant A, X2 is the average thickness in quadrant B, and so on, with u being the average thickness of the entire silicon wafer. When the thickness morphology meets the above measurements, the processing morphology is stable; when it does not, it indicates a large deviation in the thickness morphology, and the parameters need to be adjusted.

[0021] The present invention can achieve the following effects:

[0022] This invention provides an adjustment feedback method for improving the flatness stability of silicon wafers. Compared with existing technologies, it features convenient operation and good operational stability. It solves the problem of poor flatness fluctuation stability during processing. By checking silicon wafer warpage and thickness before polishing, monitoring key processing parameters, and real-time monitoring of flatness levels after polishing, the stability of the silicon wafer flatness process is ensured. Through the feedback adjustment method, the TTV level reaches below 100nm, with a standard deviation of less than 3. Detailed Implementation

[0023] The technical solution of the invention will be further described in detail below through examples.

[0024] Example: An adjustment feedback method for improving the flatness stability of silicon wafers, comprising the following steps:

[0025] Step 1: Warp control and thickness control before polishing. Before polishing, the silicon wafers are measured by the equipment to screen out those that do not meet the requirements and sort them by thickness. Then, double-sided polishing is used.

[0026] Silicon wafer warpage has a significant impact on flatness, especially the morphology after wire cutting; the average warpage deformation after wire cutting should be less than 8µm. Simultaneously, the wire cutting edge requirements are: V-shaped edge with an included angle greater than 90°; L-shaped edge with an included angle greater than 45°.

[0027] The processing method involves processing 15 silicon wafers simultaneously per batch, with the amount of material removed controlled by laser thickness measurement. If the thickness uniformity of the 15 silicon wafers is >0.8μm, there will be significant fluctuations in the flatness among the 15 wafers.

[0028] Step 2: During the polishing process, slight fluctuations in polishing slurry temperature, pH, flow rate, removal rate, and platen cooling temperature need to be controlled. The FDC system monitors and alarms these parameters: polishing slurry temperature <0.5℃, pH <0.2, flow rate <0.4L / min, removal rate >0.5μm / min, and platen cooling temperature <0.2℃.

[0029] Step 3: Perform measurement feedback adjustments to monitor and adjust the flatness level fluctuations and silicon wafer thickness morphology.

[0030] Step 4: When the silicon wafers are processed and flatness is measured, the equipment is adjusted according to the set target value. If the TTV measurement changes by more than 40nm compared to the previous batch, the machine will make appropriate corrections. If the change is +40nm, the corresponding method is to decrease the target thickness by 0.1μm, and vice versa.

[0031] Step 5: Using software analysis, monitor the thickness and morphology of the measured silicon wafers to ensure consistent thickness and morphology throughout the processing. The silicon wafers are divided into different radial regions: R1 = 80, R2 = 100, and R3 = 140. Each region is further divided into four quadrants, and the thickness of each quadrant is calculated separately. Significant deviations in thickness and morphology will cause fluctuations in the thickness values ​​of each region. Monitoring the thickness and morphology ensures the stability of flatness.

[0032] For radial calculations, the following conditions must be met: ATR1>ATR2>ATR3>0; ATR1 is AVTHKR1, the average thickness of circle R1; ATR2 is the average thickness within the R2-R1 pattern; and ATR3 is the average thickness within the R3-R2 pattern.

[0033] Regional calculations must meet the following requirements. X1 equals the average thickness in quadrant A, X2 is the average thickness in quadrant B, and so on, with u being the average thickness of the entire silicon wafer. When the thickness morphology meets the above measurements, the processing morphology is stable; when it does not, it indicates a large deviation in the thickness morphology, and the parameters need to be adjusted.

[0034] In summary, this adjustment feedback method for improving silicon wafer flatness stability is characterized by its ease of operation and good operational stability. It solves the problem of poor flatness fluctuation stability during processing. By checking wafer warpage and thickness before polishing, monitoring key processing parameters, and real-time monitoring of flatness levels after polishing, the stability of the silicon wafer flatness process is ensured. Through the feedback adjustment method, the TTV level reaches below 100nm, with a standard deviation of less than 3.

[0035] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. An adjustment feedback method for improving the flatness stability of silicon wafers, characterized in that... The following steps are included: Step 1: Warp control and thickness control before polishing. Before polishing, the silicon wafers are measured by the equipment to screen out those that do not meet the requirements and sort them by thickness. Then, double-sided polishing is used for processing. Step 2: During the polishing process, it is necessary to control slight fluctuations in polishing fluid temperature, polishing fluid pH, polishing fluid flow rate, removal rate, and plate cooling temperature. Step 3: Perform measurement feedback adjustments to monitor and adjust the flatness level fluctuations and silicon wafer thickness morphology; Step 4: When the silicon wafer is processed and its flatness is measured, the equipment is adjusted by setting the target value; Step 5: Through software analysis, monitor the thickness and morphology of the measured silicon wafers to ensure that the thickness and morphology of the processed silicon wafers are consistent; divide the silicon wafers into different radial regions with distributions of R1=80, R2=100, and R3=140; each region is divided into four quadrants, and the thickness of each quadrant is calculated separately; when there is a large deviation in the thickness and morphology, the thickness value of the region will fluctuate; Regional calculations must meet the following requirements. X1 equals the average thickness in quadrant A, X2 is the average thickness in quadrant B, and so on, with u being the average thickness of the entire silicon wafer. When the thickness morphology meets the above measurements, the processing morphology is stable; when it does not, it indicates a large deviation in the thickness morphology, and the parameters need to be adjusted.

2. The adjustment feedback method for improving the flatness stability of silicon wafers according to claim 1, characterized in that: The processing method involves processing 15 silicon wafers simultaneously in each batch, and controlling the amount of material removed during processing by laser thickness measurement. If the thickness uniformity of the 15 silicon wafers is greater than 0.8μm, there will be significant fluctuations in the flatness among the 15 silicon wafers.

3. The adjustment feedback method for improving the flatness stability of silicon wafers according to claim 1, characterized in that: The FDC system monitors and alarms parameters such as polishing slurry temperature, polishing slurry pH, polishing slurry flow rate, removal rate, and plate cooling temperature. Polishing slurry temperature fluctuation <0.5℃, pH <0.2, flow rate <0.4L / min, removal rate >0.5μm / min, and plate cooling temperature <0.2℃.

4. The adjustment feedback method for improving the flatness stability of silicon wafers according to claim 1, characterized in that: When the TTV measurement changes by more than 40 nm compared to the previous batch, the machine will make appropriate corrections; if the change is +40 nm, the corresponding method is to decrease the target thickness by 0.1 μm, and vice versa.

5. The adjustment feedback method for improving the flatness stability of silicon wafers according to claim 1, characterized in that: For radial calculations, the following conditions must be met: ATR1 > ATR2 > ATR3 > 0; ATR1 is AVTHKR1, the average thickness of circle R1; ATR2 is the average thickness within the R2-R1 pattern; and ATR3 is the average thickness within the R3-R2 pattern.

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